One notebook may contain a line from a book, a question from a conversation and a sketch of a shop window. The entries arrived on different days, but they might all have something to say about the same subject.
You can use a commonplace notebook for this kind of collection: ideas from different places, kept with enough context to revisit and connect them. The aim is to build a reference you can work with. It is fine if some pages are quotations and others are mostly your own objections.
A reading notebook follows your encounter with a particular book. Here, the subject leads. When you want to think about teaching, cooking or designing a small room, you can gather relevant entries even when their sources have little else in common.
Choose what earns a place
You could copy every interesting passage you encounter. The difficulty arrives later, when you have to search through them. Start with a few subjects you already care about or questions you are trying to answer.
Before making an entry, finish this sentence in your own words: "I want to keep this because..." You might want to test a method, challenge an assumption or remember an example. You can leave room for a thought that simply interests you, but knowing why it caught your attention makes the future note easier to use.
Keep the entry as short as the idea allows. A paragraph of source material may need only a sentence of summary. A diagram might need a caption and a reference. You are allowed to return to the original for the rest.
Make the source easy to trace
For a book, record the author, title and page or section. For an article, include the title, author where available and the URL. If a web address is too long to write comfortably, keep it in a digital reference list and give the notebook the matching reference number.
Use quotation marks for exact words and clearly label a summary. Put your response in a separate paragraph. The distinction becomes especially useful when you later write something of your own and need to know which phrasing belongs to someone else.
For a conversation, note the context without filling a personal notebook with someone else's sensitive information. If you cannot verify the wording, record it as your recollection rather than an exact quotation.
An observation is different again. "The shelf labels were hard to read from the entrance" is your observation. "Customers could not find the section" would require evidence about what those customers experienced. Keep the note within what you actually saw.
Use an index that can grow
Number your pages and reserve a few pages for an index. Begin with ordinary subject names. If an entry belongs under "Teaching", add its page number there. If it also belongs under "Questions", you can list the same page in both places.
Do not divide an empty notebook into fixed sections unless you know you need them. One subject can fill its allowance while another leaves pages unused. Writing in order and indexing afterwards leaves the space available for whatever comes next.
When an index page fills, continue it elsewhere and write the new page number at the bottom. The system can be untidy and still work, provided the references lead somewhere definite.
Avoid building a vocabulary of categories before you have any entries. A category becomes useful when it helps you find something you already have.
Add connections in plain language
When you notice a relationship, write what the relationship is. "See page 18" gives you a destination. "Compare with page 18: the same advice, but for a group rather than one person" explains why you should go there.
Connections can be disagreements. Two writers may use the same word differently or recommend opposite actions under different conditions. Keep the conditions visible. Smoothing the ideas into one agreeable summary can remove the reason they were interesting.
If an entry suggests an experiment, name a small one. A note about clearer instructions might lead you to rewrite the first paragraph of a document and ask someone where they get stuck. Record what happened beside the idea if you try it.
Open the notebook with a question
You do not need to reread the whole collection every Sunday. Use it when a relevant question arises. Look up the subject, follow the references and bring the useful entries onto a fresh page.
Write your current answer underneath them. If nothing in the collection helps, that tells you what you still need to find out. If an old note no longer convinces you, add the reason instead of quietly treating it as settled knowledge.
The next entry can then carry more than another borrowed sentence. It can record how your own view changed, with a route back to the material that changed it.